1. Field of the Invention
This invention relates to a cross point switch mounted on a device such as a telephone.
2. Description of the Related Art
A cross point switch is mounted on a device such as a telephone. The cross point switch is a switch which enables connection of any desired one of input pins and any desired one of output pins, and has a configuration as shown in FIG. 5A, for example. This configuration is substantially the same as that disclosed in U.S. Ser. No. 980,257 previously proposed by the inventor.
The cross point switch 10 shown in FIG. 5A is formed as an 1C having 24 pins. The cross point switch 10 has 64 switches S1-S64 disposed so as to form an 8.times.8 switch matrix. Turning on/off of the switches S1-S64 is controlled by a 64-bit shift register 12 and a 64-bit data latch 14. Each of the switches S1-S64 consists of an analog switch 16 and a resistor 18 as shown in FIG. 5B.
Serial data DIN input through the 21st pin is shifted left one bit by the shift register 12 at the timing of a clock CLK input through the 22nd pin. The resultant 64-bit parallel data is latched by a latch signal LATCH input through the 23rd pin. The switches S1-S64 are turned on/off according to outputs of the data latch 14. For example, if the first bit of the data latch 14 is high, the switch S1 is turned on; if low, the switch S1 is turned off. A signal input through the 24th pin, RST, is a reset signal of the data latch 14.
The cross point switch 10 further includes eight input amplifiers 20-1 to 20-8, eight output amplifiers 22-1 to 22-8, and a bias circuit 24. Each of the input amplifiers 20-1 to 20-8 supplies corresponding one of signals IN1 to IN8 input through one of the fifth to twelfth pins via eight switches to the output amplifiers 22-1 to 22-8. For example, an output of the input amplifier 20-1 is supplied via switches S1, S9, S17, . . . , S57 to the output amplifiers 22-1, 22-2, 22-3, . . . , 22-8. The output amplifiers 22-1 to 22-8 output signals supplied via eight switches through the twentieth to thirteenth pins as signals OUT1 to OUTS. The bias circuit 24 receives supply voltage VCC through the second pin, then supplies bias voltage VB to the input amplifiers 20-1 to 20-8 and the output amplifiers 22-1 to 22-8 and also outputs the voltage VB through the third pin.
The switches S1 to S64 are turned on/off in response to data DIN, as described above. For example, if only the switch S1 is turned on and switches S9, S17, . . . , S57 are turned off, an output of the input amplifier 20-1 is input to the output amplifier 22-1, but not to the output amplifiers 22-2 to 22-8. Therefore, mounting the cross point switch 10 enables any desired signal to be supplied to any desired circuit in a device such as a telephone.
The output amplifiers 22-1 to 22-8 also have a mixing function. For example, if switches S1 and S2 are turned on, outputs of the input amplifiers 20-1 and 20-2 are mixed by the output amplifier 22-1 for outputting as signal OUT1. Further, since the input amplifiers 20-1 to 20-8 exist, even if a plurality of switches corresponding to a single output amplifier 22 are turned on at the same time, signal leakage via these switches does not occur.
However, the cross point switch having the above configuration introduces a problem of high consumption current because all circuits of input amplifiers, output amplifiers, etc., always operate. In other words, all circuits must be operated even for the minimum operation of connecting a handset of a radio controller of a telephone to a telephone line; high current required for the operation of all circuits must be supplied and the power efficiency of the circuitry becomes poor. This problem becomes remarkable particularly when a commercial power supply fails. To deal with high consumption current when the commercial power supply fails, since the telephone line power is not enough, a battery must be used, leading to necessity for mounting it on a device such as a telephone.